The present invention relates to aircraft fuel systems and, more particularly, to an improved means of calculating hydraulic pump flow for detection of significant overboard leaks from a hydraulic system.
Aircraft fuel systems occasionally develop fluid leaks, such as during battle. The General Electric F414 engine proposes to use a fuel operated nozzle hydraulic pump. In this configuration, the pump, all actuators, and all hydraulic lines are filled with engine fuel at high pressure. If there is a significant hydraulic leak for any reason, then the aircraft fuel tank could be drained overboard. This can occur with any high pressure fuel hydraulic system.
Significant overboard leaks from a fuel hydraulic system, including engines employing axisymmetric vectoring exhaust nozzles, can drain the aircraft fuel tank before they are detected. Present day hydraulic systems using hydraulic fluids other than fuel are limited by the capacity of the hydraulic tank, typically under three gallons. Today, significant leaks are detected by visual means or by unusual behavior of an engine. However, when the engine operates normally in the presence of a leak, the hydraulic system increases flow up to the capacity of the hydraulic pump before the hydraulic pressure falters, and a leak can exist without detection.
It is therefore highly desirable and an object of the present invention to provide a means of detecting significant hydraulic leaks in any hydraulic system using any fluid, including oil or fuel.
Another object of the present invention is the provision of accurate pump flow measurements, making the present invention particularly adaptable for use with a system having an axisymmetric variable exhaust nozzle (AVEN). The accuracy of pump flow can be used to optimally determine hydraulic priority for an AVEN system.
Another object of the present invention is the provision for calculating and storing a flow level for servo flows. In a variable pressure system, these vary enough to create system tolerances which either open the threshold of leak detection, or, for axisymmetric variable exhaust nozzle systems, add to the flow capacity which cannot be consistently used.
These objects and other features and advantages will become more readily apparent in the following description when taken in conjunction with the appended drawings.